Astronomers have observed a white dwarf — a tightly packed, Earth-sized stellar ember — that is creating a colorful shock wave as it moves through space, leaving them searching for an explanation.
The highly magnetized white dwarf is gravitationally bound to another star in what is called a binary system. The white dwarf is absorbing gas from its companion as they orbit close to each other. The system is located in the Milky Way, about 730 light years from Earth—relatively close in cosmic terms—in the constellation Auriga.
A light year is the distance that light travels in one year, 9.5 billion km.
The shock wave – more specifically a bow shock – caused by the white dwarf was observed using the Very Large Telescope of the European Southern Observatory, based in Chile. The shock wave was seen in an image released by scientists glowing in various colors produced when material flowing outward from the white dwarf collided with interstellar gas.
“A shock wave is created when a fast-moving material is thrown into the surrounding gas, suddenly compressing and heating it. A bow shock is the curved shock front that forms when an object moves rapidly through space, similar to the wave in front of a ship moving through water,” said astrophysicist Simone Scaringi of Durham University in England, co-lead author of the study published Monday in the journal Nature Astronomy.
“The colors come from interstellar gas that is heated and excited by the impact. Different chemical elements glow with specific colors when this occurs,” Scaringi added.
In this shock wave, a red hue represented hydrogen, green nitrogen, and blue oxygen residing in interstellar space.
Other white dwarfs have been observed to generate shock waves. But all of those were surrounded by gas disks siphoned from a binary partner. Although this white dwarf is absorbing gas from its companion, it lacks that disk and is releasing gas into space for unknown reasons.
White dwarfs are among the most compact objects in the universe, although not as dense as black holes.
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Stars with up to eight times the mass of the sun seem destined to end up as white dwarfs. Finally they consume all the hydrogen they use as fuel. Gravity then causes them to collapse and shed their outer layers in a “red giant” stage, ultimately leaving a compact core: the white dwarf.
“There are a lot of white dwarfs out there, since these are the most common extremes of stellar evolution,” Scaringi said.
The sun seems destined to end its existence as a white dwarf within billions of years.
This white dwarf has a mass comparable to that of the Sun contained in a body slightly larger than Earth. Its binary companion is a type of low-mass star called a red dwarf, which is about a tenth the mass of the sun and thousands of times less luminous. It orbits the white dwarf every 80 minutes, with both extremely close to each other, about the distance between the Moon and Earth.
The gravitational force of the white dwarf is pulling gas out of the red dwarf. This siphoned material is absorbed toward the white dwarf along its strong magnetic field, eventually reaching its magnetic poles. Although this process releases energy and radiation, it cannot explain the flow of material necessary to produce the observed shock wave, Scaringi said.
“Every mechanism with gas coming out doesn’t explain our observation, and we remain puzzled by this system, which is why this result is so interesting and exciting,” Scaringi said.
“The shape and length of the (blast) structure demonstrate that this process has been ongoing for at least 1,000 years, making it a long-lived event and not an isolated event,” Scaringi added.
The researchers took note of the aesthetics of the colorful shock wave.
“Beyond the science, it is a striking reminder that space is not empty or static as we naively imagine: it is dynamic and sculpted by movement and energy,” Scaringi said.
With information from Reuters
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